The present disclosure relates generally to an axial piston pump and, more particularly, pertains to a pump having an improved holddown system which provides for proper loading of the pump components, and enables a smoother, quieter and more balanced pump operation.
Axial piston pumps are old and well known in the art. All such pumps include a swashplate (thrust plate) against which axial piston ends of piston assemblies bear, and along which such ends rotate with an angled reaction surface of the swashplate allowing a cyclic reciprocal movement of the pistons in the piston assemblies providing each piston-holding cylinder with low pressure intake and high pressure discharge of hydraulic fluid on each rotation. The swashplate (thrust plate) is mounted for rotation on a tilt axis transverse to a longitudinal axis of a drive shaft which drives a cylindrical rotor housing the pistons. Axial piston pumps rely on different designs or holddown systems for holding a rear end of the rotor against the valve plate and/or port end cover connected to a pump housing, and maintaining slipper shoes on the piston ends against the swashplate (thrust plate).
One traditional piston pump design incorporates a compression (holddown) spring inside the rotor, and utilizes transfer rods or pins (typically a set of three) to transmit the compression spring force to a spherical ring. The spherical ring engages a holddown plate that maintains the piston assemblies against the swashplate (thrust plate), and the rotor against the valve plate and the port end cover forming an action/reaction arrangement. The holddown spring, rods, spherical ring and holddown plate all rotate with the drive shaft, rotor and piston assemblies.
Another piston pump design employs a piston (holddown) spring inside of each piston assembly to hold the rotor against the valve plate, and each piston assembly against the swashplate (thrust plate). Again, the holddown springs rotate with the drive shaft, rotor and the piston assemblies.
In optimizing axial piston pump performance, it is critical to keep the rotor balanced for smooth and quiet pump operation. Unfortunately, it has been found that these previous pump designs require more than a desired amount of rotating parts which, when connected towards the rear of the pump outside the swashplate, cause rotor imbalance and weight problems that can negatively affect pump performance.
Therefore, it is desirable to provide a holddown system for an axial piston pump which loads the pump components in a manner which will keep the rotor balanced and ensures smooth, quiet operation of the pump. It is also desirable to provide an axial piston pump which reduces the number of pump components and simplifies pump manufacture and assembly.